Fiber optics transmission is the medium of choice for voice and data service provider networks. At the current time, fiber optics provides the highest bandwidth per unit cost of any transmission medium. Early fiber optic systems, however, used proprietary architectures, equipment line codes, multiplexing formats, etc., such that one fiber optic system could not be connected to another unless they were both from the same manufacturer.
In response, the “Synchronous Optical Network” standard, commonly called “SONET”, was developed in the U.S. to provide a standard for connecting one optical fiber system to another. SONET (and the virtually identical international standard, “Synchronous Digital Hierarchy” or “SDH”) provides specifications for digital transmission bandwidths that formerly were not possible. By using equipment that conform to this standard, service providers can use their currently embedded fiber optic networks to effect higher bandwidth over the same fiber. However, equipment (commonly called “nodes”) that can provide add-drop and through switching of SONET-based communications at the wide bandwidth end of the specification is generally unavailable.